1. Field of the Invention
The present invention relates to various kinds of electronic information devices such as digital cameras, TV sets, personal computers, electronic books, man-machine interfaces, etc, and a control method of such a device.
2. Description of Related Art
With development of electronic information devices which require a display section to display images, such as computers, digital cameras, etc., various display devices using materials with a memory effect have been developed. For example, Japanese Patent Laid Open Publication No. 8-317324 describes an embodiment of adopting ferrodielectric liquid crystal to an electronic camera. Japanese Patent Laid Open Publication No. 10-197850 describes an embodiment of using ferrodielectric liquid crystal in a display device for a pen computer so as to save energy.
Such a display device using a material with a memory effect has an advantage of consuming no electric power in maintaining a picture on the display, while consuming electric power in writing information on the display. For example, Japanese Patent Publication No. 7-101336 discloses that a supply of electric power to a display panel with a memory effect is shut off after the display panel has made a display of a calendar, a picture, etc.
In the display device disclosed by Japanese Patent Publication No. 7-101336, however, if a supply of electric power is shut off during image writing on the display, an incompletely written picture stays on the display, which is ugly. Thus, in such a display device using a material with a memory effect, the display sequence must be changed. There is no prior art which focuses on a power-down during image writing on a display with a memory effect. If a supply of electric power is shut off suddenly, there may be a case that an incompletely written image is displayed continuously. In order to avoid such trouble, it is necessary to time a power-down of the display section to completion of image writing on the display, which is inconvenient.
Conventionally, only ferrodielectric liquid crystal is regarded as a material with a memory effect. Recently, however, cholesteric liquid crystal and chiral nematic liquid crystal start to be used practically. For example, U.S. Pat. No. 5,625,477 discloses a method of displaying a multi-tone image on chiral nematic liquid crystal.
Accordingly, in the art of display devices using materials with a memory effect, it is required to improve the control of image writing and power off so as to display a complete picture at all times. Further, in the art of electronic information device used as a man-machine interface which has an input section (including a power switch) with which an operator inputs a specified command and a display section with a memory effect, it is necessary to improve the association of the input section with the display section to improve the operability.